Japanese Laid-Open Patent Publication (unexamined) No. 8-240373 discloses a conventional refrigerator as shown in FIG. 1, which includes a refrigerator body 1 having a refrigerator compartment 2 and a freezer compartment 3 both defined therein for storing foods. The refrigerator compartment 2 and the freezer compartment 3 are partitioned by a generally horizontally extending medial wall member 30 and are opened and closed by doors 4 and 5, respectively, hingedly mounted on a front surface of the refrigerator body 1.
A freezer cooling unit 8 is disposed on the rear side of the freezer compartment 3 for cooling air drawn from the freezer compartment 3 using the latent heat of evaporation of refrigerant. An air fan 7 connected to a rotary shaft of a fan motor 31 is disposed above the freezer cooling unit 8 for circulating into the freezer compartment 3 cold air heat-exchanged by the freezer cooling unit 8.
A plurality of shelves 32, on which foods are placed, are accommodated within the refrigerator compartment 2 to partition it into a plurality of small compartments. A low-temperature storage chamber 33, in which specific foods are stored at a specific temperature range, is defined at an upper portion of the refrigerator compartment 2, while a vegetable storage chamber or crisper 6 is defined at a lower portion of the refrigerator compartment 2. A compressor 11 is disposed in a machine chamber positioned below the vegetable storage chamber 6.
A cold air discharging means 34 is provided on the rear side of the refrigerator compartment 2, while a duct member 36 having cold air outlets 35 defined therein is provided on the rear side of the low-temperature storage chamber 33. A refrigerator cooling unit 10 is disposed on the rear side of the duct member 36 for heat-exchanging air drawn through an air passage 37, while an air fan 9 connected to a rotary shaft of a fan motor 39 is disposed above the refrigerator cooling unit 10 so that the air drawn through the air passage 37 may be heat-exchanged by the refrigerator cooling unit 10 and introduced into the refrigerator compartment 2 and the low-temperature storage chamber 33 through cold air outlets 38 and through the cold air outlets 35, respectively.
The cold air discharging means 34 communicates at an upper portion thereof with a lower portion of the duct member 36 and extends downwardly to a rear portion of the vegetable storage chamber 6.
In the above-described conventional construction, however, the temperature within the low-temperature storage chamber 33 depends on the distribution ratio of air discharged from the cold air outlets 35 and 38. Accordingly, when the heat load in the refrigerator compartment 2 is low, for example, when the temperature of the open air is low, the working efficiency of the air fan 9 becomes low, making it impossible to cool the low-temperature storage chamber 33 down to a set temperature. Furthermore, if the low-temperature storage chamber 33 is cooled down to the set temperature, the temperature within the refrigerator compartment 2 becomes lower than a set temperature, thus causing a problem of having to heat the refrigerator compartment 2 by the use of, for example, a heater.
In addition, even after the air fan 9 has stopped upon completion of the cooling of the refrigerator compartment 2, the cooling of the freezer compartment 3 continues and, hence, air in the proximity of the refrigerator cooling unit 10 is cooled by a refrigerant flowing through the refrigerator cooling unit 10. Because the cooled air flows downwardly from the refrigerator cooling unit 10 by convection, the cold air flows from the cold air outlets 38 into a lower portion of the refrigerator compartment 2, thus causing a problem of lowering the temperature of the lower portion of the refrigerator compartment 2 below a set temperature.
Japanese Utility Model Publication (examined) No. 58-35979 discloses another conventional refrigerator employing a refrigerating cycle as shown in FIG. 2.
In FIG. 2, 41 is a compressor, 42 a condenser, 43 a first capillary serving as a means to reduce pressure, 44 a first evaporator for cooling a refrigerator compartment, 45 a second evaporator for cooling a freezer compartment, and 46 a channel control valve. 47 is a second (bypass) capillary connecting a flow-dividing portion 48 positioned between the first capillary 43 and the channel control valve 46 with a flow-merging portion 49 positioned between the first evaporator 44 and the second evaporator 45. 50 is a third capillary provided between the channel control valve 46 and the first evaporator 44.
Thus, the refrigerating cycle is repeatedly started and stopped in order to cool a freezer compartment and a refrigerator compartment (not shown) and to maintain them at comparatively low temperatures.
During the operation of the refrigerating cycle, a refrigerant compressed by the compressor 41 is condensed and liquefied in the condenser 42. When the channel control valve 46 is opened, the condensed refrigerant, whose pressure is lowered by the first capillary 43, reaches the flow-dividing portion 48 in a medium-pressure state. The refrigerant is then divided at the flow-dividing portion 48 to flow through the second capillary 47 and the third capillary 50.
Part of the refrigerant is reduced in pressure by the third capillary 50, vaporized or gasified by the first evaporator 44 and the second evaporator 45, and reabsorbed by the compressor 41. The other part is reduced in pressure by the second capillary 47, merged at the flow-merging portion 49, and vaporized or gasified by the second evaporator 45.
The third capillary 50 has a much lower resistance than does the second capillary 47 and, hence, most of the refrigerant passes through the third capillary 50 when the channel control valve 46 is open.
In addition, when the channel control valve 46 is in a closed state, the condensed refrigerant is reduced in pressure by the first capillary 43 and the second capillary 47, vaporized or gasified by the second evaporator 45, and absorbed by the compressor 41.
The interior of the refrigerator is cooled by heat exchange with the evaporators whose temperature is lower in comparison with the temperature inside the refrigerator.
In such a refrigerator, however, the refrigerant whose pressure has been lowered by the first capillary 43 during the opening of the channel control valve 46 is temporarily expanded when divided at the flow-dividing portion 48, and is then readmitted into the comparatively narrow capillaries.
The refrigerant at the flow-dividing portion 48 is a two-phase refrigerant composed of a gas and a liquid. Because the refrigerator experiences wide-ranging load variations due to changes in the temperature of outside air, the opening and closing of the door, the introduction and removal of food products, and the like, the flow rate in the capillaries also varies, changing the dryness of the refrigerant at the flow-dividing portion 48.
Because the flow rate in a capillary decreases when the gas phase of the refrigerant enters an inlet portion thereof, the flow rate of the third capillary 50, which normally allows essentially all of the refrigerant to pass through, sometimes decreases and the flow rate through the second capillary 47 increases when a difference in resistance arises between the second capillary 47 and the third capillary 50; for example, when one of them is filled with a liquid and the other is in a state in which a gas enters the inlet portion. The same applies to the transitional period of opening or closing the channel control valve 46 due to the changes in the inlet state of the capillaries.
A disadvantage is that due to such flow rate variations, the flow rate of the refrigerant through the first evaporator 44, which is used for the cooling of the refrigerator compartment, is insufficient when such cooling is needed, and the refrigerator compartment is not cooled properly.
Another disadvantage is that because the heat capacity from the flow-dividing portion 48 to the channel control valve 46 is comparatively high, these portions are heated by the ambient temperature when the compressor 41 is stopped, dryness is enhanced during operation, the flow rate into the comparatively narrow capillaries decreases, and the cooling performance is adversely affected.
In addition, the medium pressure of the flow-dividing portion 48 is set high in comparison with the vaporization pressure of the evaporator in order to reduce the frosting of the channel control valve 46, so the third capillary 50 must have a predetermined resistance value (resistance value close to the first capillary 43), and the second capillary 47 must have an even higher resistance value in order to divide the flow when the channel control valve 46 is open. Furthermore, the total resistance value of the capillaries is such that a series connection is established between the first capillary 43 and the second capillary 47 when the channel control valve 46 is closed, and a combination of a series connection with the first capillary 43 and a parallel connection between the third capillary 50 and the second capillary 47 is formed when the channel control valve 46 is opened.
Since resistance is lower for a parallel connection than for each individual element, the difference in the overall resistance of the refrigerating cycle between the open and closed states of the channel control valve 46 is extremely large. The reduced-pressure resistance of the refrigerating cycle is therefore optimized only when the channel control valve 46 is open or closed, resulting in lower system efficiency.
Yet another drawback is that the cooling system circuits can be switched by opening and closing the channel control valve 46, but when a switch over is made from a circuit that passes through the first evaporator 44 for the cooling of the refrigerator compartment to a circuit that creates a bypass through the second evaporator 45 for the cooling of the freezer compartment, the refrigerant present in the first evaporator 44 moves into the second evaporator 45, and if the arrangement is such that the first evaporator 44 is disposed below the second evaporator 45, or the line-pass pattern of the first evaporator 44 has a structure in which a liquid trap is formed (for example, a structure whose pass pattern is such that a plurality of rows or tube runs go from top to bottom and then back to the top), the refrigerant is propelled as a result of vaporization and condensation rather than being propelled directly in the liquid state, so a comparatively long time elapses and the machine oil tends to stay in the first evaporator, necessitating an increase in the amount of sealed machine oil.
Another feature is that, for example, a top-freezer refrigerator is configured such that the first evaporator is disposed below the second evaporator, but because the refrigerant and the machine oil present in the first evaporator when the channel control valve is closed have difficulty returning to the second evaporator in the top position and tend to stay in the first evaporator due to the effect of gravity, the system tends to operate with an insufficient amount of refrigerant or machine oil following valve switching, creating drawbacks in terms of cooling performance or compressor reliability.
A drawback, therefore, is that a gas deficit is created during the switching of the channel control valve 46, or the refrigerant must be sealed in a larger amount, leading to increased electric consumption and higher costs.
Still another drawback is that the cooling system must be welded in a larger number of locations, and costs are increased as a result of increased labor requirements.
The present invention has been developed to overcome the above-described disadvantages.
It is accordingly an objective of the present invention to provide an improved refrigerator capable of properly regulating the temperature within a low-temperature storage chamber independently of load variations and preventing a refrigerator compartment from reducing in temperature below a set value.
Another objective of the present invention is to provide a refrigerator having an enhanced cooling performance.
Yet another objective of the present invention is to provide a refrigerator having optimally designed pressure reduction means and a more effective cooling system.
Still another objective of the present invention is to provide a refrigerator capable of reducing a gas deficit during the switching of a channel control valve and rendering the cooling system more effective.
A further objective of the present invention is to provide a low-cost refrigerator for which less labor is needed to assemble the cooling system.